"You'll need a new app to open this file" is probably the most common error faced by millions of Windows users every day. This is either because the program required to open a file is not available on your system or there may be other issues.

What is .DMB file extension?

Game file used by BYOND, a program used for running games created with the BYOND development tools; saves a game executable that can be run on the player's computer; used for storing 2D multiplayer online games.
To host an online BYOND game, choose File ? Open File... and then select your DMB file from the dialog box.
NOTE: Many games are available for download from the BYOND website, but an account is required to download and play them.
You can see a list of software programs here on easyfileopener.org that can open this file type so that you don’t need to search for it on the web. You can then open your file with this extension using a software listed below.